Autism spectrum disorder and intellectual disability (ASD/ID) are severe neurodevelopmental conditions with early childhood onset. Advances in genetics have illustrated that ASD/ID represent a spectrum of rare disorders and that mutations in hundreds of genes may result in susceptibility to ASD/ID. This heterogeneity represents significant challenges but at the same time unique opportunities for research in the field of ASD/ID. Many of the genes implicated in ASD/ID appear to converge on a few common pathways, suggesting that there may be a common dysfunction at the cellular or systems level. Deeper understanding of the shared pathophysiology of these diseases may serve as gateways for understanding mechanisms of other causes of ASD/ID and for shared treatment possibilities. Here we focus of three well-established genetic syndromes that are associated with high penetrance for ASD/ID: TSC1/2, PTEN and SHANK3 mutations. Specific aims for TSC are: 1) characterize the developmental phenotype of ASD and ID in a large cohort of pediatric patients with TSC; 2) identify biomarkers using advanced MR imaging; 3) establish infrastructure for the collection and storage of human bio-specimens, including genetic material, from TSC patients and their family members with ASD. Specific aims for PTEN are: 1) determine cross-sectional and longitudinal medical, behavioral, and cognitive differences between PTEN ASD and other groups; 2) identify cognitive, neural systems, and molecular biomarkers specific to PTEN ASD; 3) create and maintain a biorepository and linked phenotypic database for PTEN ASD. Specific aims for SHANK3 are: 1) characterize PMS using standardized medical, behavioral, and cognitive measures and to track the natural history of the syndrome using repeated longitudinal assessments; 2) identify biomarkers using advanced MR imaging; 3) identify genetic factors which contribute to diverse phenotypes in patients with PMS. As detailed in the Resources sections, this Consortium involves experienced physician-researchers from premier academic institutions with strong institutional support, impressive mentors for training of future physician-researchers, and long-standing connections to patient advocacy organizations with extensive recruitment networks.